This post is based from Did the Reagan-era USDA really classify ketchup as a vegetable? - The Straight Dope
Perhaps of interest is that ketchup and salsa are not the federal government’s first attempts to classify (or rather misclassify) non-vegetables as vegetables. Long before ketchup and salsa, tomatoes, though scientifically classified as fruit, were officially classified as vegetables by the U.S. Supreme Court in the case of Nix v. Hedden (1893). The Court stated in pertinent part:
"Botanically speaking, tomatoes are the fruit of a vine, just as are cucumbers, squashes, beans, and peas. But in the common language of the people, whether sellers or consumers of provisions, all these are vegetables which are grown in kitchen gardens, and which, whether eaten cooked or raw, are, like potatoes, carrots, parsnips, turnips, beets, cauliflower, cabbage, celery, and lettuce, usually served at dinner in, with, or after the soup, fish, or meats which constitute the principal part of the repast, and not, like fruits generally, as dessert.
The attempt to class tomatoes as fruit is not unlike a recent attempt to class beans as seeds, of which Mr. Justice Bradley, speaking for this court, said: 'We do not see why they should be classified as seeds, any more than walnuts should be so classified. Both are seeds, in the language of botany or natural history, but not in commerce nor in common parlance. On the other hand in speaking generally of provisions, beans may well be included under the term ‘vegetables.’"